1. Field of the Invention
The invention relates to an oil passage structure of a valve operating system for an internal combustion engine, in which an oil passage used for controlling a variable valve timing mechanism is provided in a cam journal for a camshaft.
2. Description of the Related Art
Each of Japanese Patent Application Publications No. 2000-220420 (JP-A-2000-220420), No. 09-273404 (JP-A-09-273404), No. 09-291805 (JP-A-09-291805) and No. 2000-179311 (JP-A-2000-179311) describes invention relating to a variable valve timing mechanism (hereinafter, referred to as “VVT”) for an internal combustion engine.
Each of the above-described publications describes an oil passage structure in which control oil passages for VVT are provided in a first cam journal at the front end of a camshaft, and an oil passage for a hydraulic lash adjuster (hereinafter, referred to as “HLA”) is provided in a cam journal at the rear end of the camshaft, or at the rear end of a rocker shaft. These oil passages are constituted by oil grooves in the cam journals. Each of the oil grooves is formed using a die-casting die.
It is rational to provide the two control oil passages used for controlling VVT (i.e., a timing-advance oil passage used for advancing a valve timing, and a timing-retard oil passage used for retarding the valve timing) in the first cam journal that is close to a timing pulley (sprocket). Also, the oil passage used for controlling HLA needs to be separated from the oil passages used for controlling VVT. Further, it is difficult to further provide the oil passage used for supplying oil to the intake HLA and/or exhaust LA in the first cam journal. Therefore, the oil passage for the intake HLA and/or exhaust HLA needs to be provided in the other cam journal.
More specifically, because the oil is generally supplied from the main gallery of the engine to the first cam journal through the control passages used for controlling VVT, the oil passage used for supplying the oil to HLA is provided in another cam journal at the rear end of the engine. However, when this oil passage structure is employed, the oil passage that extends in a longitudinal direction of the engine needs to be provided at the rear end side of the engine (cylinder block). This increases the overall length of the engine. Also, there is no enough space in the portion of the first cam journal at the front side of the engine, it is difficult to provide the oil passage for HLA in addition to the two control passages for VVT at the front end side of the engine. When an oil supply passage for an oil jet is provided, the same problem may arise.
When the oil passage for HLA, or the oil passage for the oil jet is provided in addition to the control oil passages for VVT, the oil passage that extends in the longitudinal direction needs to be provided at the rear end side of the engine (cylinder block). This increases the overall length of the engine. This is the problem to be solved by the invention.